Preselector system



Jan. 25, 1938. D. v. SINNING ER PRESELECTOR SYSTEM P Auuno.

Demo

Filed Feb. 11, 1936 DEMO.

Osc.

Pree- FSELECTOE INVENTOR. DW/GHTM j/NN/NGER.

BY I

A QI'ORNEY,

Patented Jan. 25, 1938 UNITED STATES PATENT orricc 2,100,229 I Dwight V. sinningen chicago, 11].,

Johnson Laboratories, Inc., Chicago,

assign'or to 111., a

corporation of Illinois I Application February 11, 1936, Serial No. 83,295

12 Claims.

The invention relates to high-frequency circuits and more particularly to those employed in receiving systems of the superheterodyne type, where the signal passes through several circuits tuned to the signal frequency, is modulated with locally produced oscillations, then is demodulated and amplified at an intermediate frequency, and finally is demodulated again and rendered audible. The part of the system through which the in signal passes without a change in frequency usually includes an antenna circuit and one or two -resonant circuits with or without a thermionic amplifier tube, and may be termed the pre-selectorsystem is largely due to the efliciency of the intermediate-frequency amplifier which, being operated at a fixed frequency, may be designed to have a desired selectivity characteristic. The prethe desired signal, to aid in the rejection of undesired signals in adjacent channels, and to sub,- stantially reject signals of certain other frequencies to which a superheterodyne receiver tends ,to respond.

One of the objects of the invention is to provide a simple, inexpensive, and efficient system of pre-selection. Another object of the invention is to so shape the selectivity characteristic of the pre-selector that the receiver is particularly adaptable for high-fidelity reception, that is, not discriminatoryagainst the higher modulation frequencies of the incoming signal. object of the invention is to produce a sufficiently great signal gain between the antenna and the input to the first demodulator as to insure a high signal-to-noise ratio. A further object of the invention is to improve the image-frequency ratio of a superheterodyne receiver and to sufficiently reject signals of the intermediate frequency of the receiver.

The invention will be better understood if reference is made to the accompanying drawing, in

which:

Fig. 1 is a block diagram radio receiver;

Fig. 2 is a schematic diagram ofthe pre-selector of a superheterodyne radio receiver embodying the invention; and

Fig. 3 is a schematic diagram of a modified form of pre-selector embodying the invention.

Referring to Fig. 1, the block diagram schematically shows the components of a superheterodyne receiver. The signal received on the antenna is fed through a pre-selector, which may of a superheterodyne tuned circuit 4. The selectivity obtainable in a superheterodyne selector of the receiving system serves to collect Still another or 'may not include a vacuum-tube amplifier, to the first demodulator. plied by the local oscillator with oscillations of such frequency that the resultant beat frequency is equal to the resonant frequency of the intermediate-frequency amplifier. The beat-frequency signal is amplified and passed through the second demodulator, where it is rectified to produce an audible component which, after suitable amplification, is delivered to the loud speaker.

Referring to Fig. 2, the antenna I is connected to ground through a high-impedance choke coil 2 and is coupled by means of capacitor 3 to the Circuit I includes iron-core inductor 5, variabletuning capacitor 6, adjustable trimmer capacitor 1, coupling winding 9, and coupling capacitor I I. Tuned circuit 8 includes iron-core inductor 5a., which is inductively coupled to winding 9, variable tuning capacitor 6a, adjustable trimmer capacitor. la, and coupling capacitor ll; Circuit 8 is in the input circuit of vacuum tube III, which is arranged to function as the first demodulator of a superheterodyne' receiver. The junction of inductor in and capacitor H is normally connected to a source of biasing potential, which may, forexample, be provided by an automatic amplification control resistor in the'output circuit of the second demodulator.

Inductors 5 and 5a are preferably of the type V which is made by employing a sectionalized-winding of Litz wire on a core of finely comminuted magnetic material. The high eiiiciency of this type of inductor permits high gain to be obtained between antenna i and circuit I with a coupling capacitor 3 of relatively low capacitance, so that changes in the electrical characteristics of antenna i have a relatively'small effect upon the resonant frequency of circuit 4. Choke coil 2 is preferably of sufficiently high inductance so that the resonant frequency of the antenna circuit is below the lowest frequency to which circuit] may be tuned, but higher than the intermediate frequency to be employed in the receiver, in order to improve the performance at the lower signal frequencies without increasing the response of the receiver to undesired signals of the intermediate frequency.

Winding 5 is so related in number of turns and spacing with/respect to inductor lie that the in- The demodulator is supthat attenuation in the pre-selector of the higher modulation frequencies of the incoming signal is avoided. Capacitor II has such a large capaci tance that the coupling between circuits 4 and 8 is substantially entirely inductive at signal frequencies, as for example between 540 and 1600 kilocycles. With this arrangement, it is possible to realize, from the antenna to the grid of vacuum tube l0, substantially half of the gain obtained between 'the antenna and the circuit 4. Circuits 4 and 8 may be simultaneously tuned to the frequency of the desired signal by mechanically ganging variable capacitors 6 and Be.

When the usual superheterodyne radio receiver is tuned to a desired signal, some response is likely to be obtained from a second signal which is higher in frequency than the desired signal by twice the intermediate frequency of the receiver. The undesired signal mg be called the imagefrequency signal. For I ample, if the desired signal has a frequency of 600 kilocycles and the intermediate frequency of the receiver is 450 kilocycles, the image-frequency signal will have a frequency of 600+(2 450) or 1500 kilocycles. The

ratio of the input voltage of image frequency re-- quired to produce a given output to the signal voltage required for the same output is called the image-frequency ratio. In the usual receiver which employs two tuned circuits in the pre-selector, the image-frequency ratio may be of the order of 3000. A feature of the present invention is to substantially raise the value of this ratio by the proper selection and arrangement of the circuit components.

Referring again to Fig. 2, circuit 4, which is tuned to the frequency of the desired signal, ap-' pears as a reactance to the image-frequency signal, and in itself offers an image-frequency ratio of about to 60. Circuit 8, being also tuned to the frequency of the desired signal, likewise ofl'ers an image-frequency ratio of the sameorder, so that the over-all image-frequency ratio of the pro-selector is about 3000. In addition, a portion of the image-frequency signal is shunted to ground through capacitor 1 and winding 9. This flow of image-frequency current through winding 9 induces in inductor 5a a voltage of image frequency whichis opposite in phase to the imagefrequency voltage normally present at the terminals of inductor 5a. By proper choice of capacitor I, the image-frequency ratio of the receiver may be increased ,by this ethod to a value of the order of 10,000 to 50,00. Alternatively, capacitor 1 may be connected as shown in Fig. 3 directly between the antenna I and the high-potential terminal of winding 9. This arrangement minimizes the effect which capacitor 1 has on the tuning range of variable capacitor 6.

The gain of the pre-selector is largely dependent upon the proper design of the antenna circuit. The nearer the resonant frequency of the antenna circuit is to the lower limit of the signal frequencies, the higher the gain obtainable. The lowest frequency of 540 kilocycles, and the intermediate frequency is usually about 450 kilocycles. 4 The resonant frequency of the antenna circuit should be so chosen,

tenna circuit will'resonate at a frequency between 450 and 540 kilocycles. If the antenna circuit resonates too near the intermediate frequency of the receiver, a signal of the intermediate frequency intercepted by the antenna may the nat ural frequency of said the broadcast band is about balance each other out. As the frequency increases, however, the inductive coupling becomes greater and the capacitive coupling decreases, so that in the signal-frequency range the coupling is substantially entirely inductive. In a particular instance, a receiver embodying the present invention was tuned to a signal frequency of 600 k ilocycles. The undesired response to a signal of 450 kilocycles, the intermediate frequency of the receiver, increased ten times when the arrangements of the invention were rendered inoperative without otherwise altering the receiver. The addition of the arrangements herein described produced only a slight decrease in the gain of the receiver at the lower signal frequencies. '1 By applying the teachings of the present invention, it is possible to design a pre-selector having high gain, a. high signal-to-noise ratio, a high image-frequency ratio and good attenuation of intermediate-frequency signals, with the use of only two variably tuned circuits. Furthermore,

a pre-selector designed in accordance with the invention provides freedom from uation of the higher modulation the incoming signal.

Having thus described my invention, what I claim is:

serious attenfrequencies 01 1. A pre-selector system for a superheterodyne receiver incl ding a fixed-tuned antenna circuit capacitors being so connected to said inductance as to increase the discrimination of said system against. signals of image frequency.

2. A pre-selector system for a superheterodyne receiver having an intermediate-frequency amplifier, said system including an antenna circuit and .flrst and second resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit, said antenna circuit including a reactor such that antenna circuit is lower than any. frequency to which said resonant circuits are tunable but higher than the frequency of said intermediate-frequency amplifier, and inductive-capacitive coupling means between said first and second resonant circuits, said lastmentioned coupling means being adapted to exclude signals of the frequency of said intermediate-frequency amplifier. by proper selection of inductor 2,, that the an-' 3. A pre-selector system for a superheterodyne receiver having an intermediate-frequency amplifler, said system including an antenna circuit and first and second resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit, said receiver having an intermediate-frequency amplifier, said system including an antenna circuit and first and second resonant circuits, variable capacitors for tuning said resonant circuits and adjustable capacitors for aligning said resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit including a reactor such that the natural frequency of said antenna circuit is lower than any frequency to which said resonant circuits are tunable but higher than the frequency of said intermediate-frequency amplifier, inductive-capacitive coupling means between said first and second resonant circuits, said last-mentioned coupling means being adapted to exclude signals of the frequency of said intermediate-frequency amplifier, one of said adjustable capacitors being connected to said last-mentioned coupling means to increase the discrimination of said system against undesired signals which differ in frequency from the desired signal by twice the frequency of said intermediate-frequency amplifier.

5. A pre-selector systemfor a superheterodyne receiver having an intermediate-frequency amplifier, said system, including an antenna circuit and first and second resonant circuits, each of said resonant circuits having ahigh-potential side and a low-potential side, variable capacitors connected from the high-potential sides of said resonant circuits to ground for tuning said resonant circuits adjustable capacitors connected from the high-potential sides to the low-potential sides of said resonant circuits to align said resonant circuits, combined inductive'and capacitive coupling means betweenv said antenna and said first resonant circuit including a reactor such that the natural frequency of said antenna circuit is lower than any frequency to which said resonant circuits are tunable but higher than the frequency of said intermediate-frequency amplifier and a winding inductively coupled to said second resonant circuit connected in series with a fixed capacitor between the low-potential side of said first resonant circuit and ground.

6. A pre-selector system for a superheterodyne receiver having an intermediate-frequency amplifier, said system including an antenna circuit and first and second resonant circuits, each of said resonant circuits having a high-potential side and a low-potential side, variable capacitors connected from the high-potential sides of said resonant circuits to ground for tuning said resonant circuits, an adjustable capacitor connected from the high-potential side to the low-potential side of said second resonant circuit to align said resonant circuit, combined inductive and capacitive coupling means between said antenna and said first resonant circuit including a reactor such that the natural frequency of said antenna circuit is lower than any frequency to which said resonant circuits are tunable but higher than the frequency of said intermediate-frequency amplifier, a winding inductively coupled to said second resonant circuit connected in series with a fixed capacitor between the low-potential side of said first resonant circuit and ground, and an adjustable capacitor connected between said antenna and the low-potential side of said first resonant circuit.

'7. A pre-selector system for a superheterodyne receiver having an intermediate-frequency amplifier, said system including an antenna circuit and, first and second resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit, said antenna circuit including a reactor such that the natural frequency of said antenna'circuit is lower than any frequency to which-said resonant circuits are tunable, and inductive-capacitive coupling means between said first and second resonant circuits, said last-mentioned coupling means being adapted to exclude signalsoi' the frequency of said intermediate-frequency amplifier.

8. A pre-selector system for a super-heterodyne receiver having an intermediate-frequency amplifier, said system including an antenna cir'-' cuit and first and second resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit, said antenna circuit including a reactor suchthat the natural frequency of said an-' tenna circuit is lower than any frequency to which said resonant circuits are tunable, inductice-capacitive coupling means between said first and second resonant circuits, s'aid last-mentioned coupling means being adapted to exclude signals of the frequency of said intermediate-frequency amplifier, and capacitance between said antennacircuit and said last-mentioned coupling means to increase the discrimi-.

nation of said system against signals of image frequency.

9. A pre-select-or system for a superheterodyne receiver having an intermediate-frequency amplifier, said system including an antenna circuit and first and second resonant circuits, variable capacitors fortuning said resonant circuits and adjustable capacitors for aligning said resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit including a reactor such that the natural frequency of said antenna circuit is lower than any frequency to which said resonant circuits are tunable, inductive-capacitive coupling means between said first and second resonant circuits, said last-mentioned coupling means .being adapted to exclude signals of the frequency of said intermediate-fre- V quency amplifier, one of said adjustable capacitors being connected to said last-mentioned coupling means to increase the discrimination of said system against undesired signals which differ in frequency from the desired signal by twice the frequency of said intermediate-frequency amplifier.

10.'A' pre-selector system for a superheteroed from the high-potential sides to the low-potential sides of said resonant circuits to align said resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit including a reactor such that the natural frequency of said antenna circuit is lower than any frequency to amplifier, said system including an antenna circult and first and second resonant circuits, each of said resonant circuits having a high-potential side anda low-potential side, variable capacitors connected from the high-potential sides of said resonant circuits to ground for tuning said resonant circuits, an adjustable capacitor connected from the high-potential side to the low-potential side of said second resonant circuit to align said resonant circuit, combined inductive and capacitive coupling means between said an- Patent 'No. 2,106,229,

CERTIFICATE OF CORRECTION.

tenna and said first resonant circuit includinga 'reactor such that the natural frequency of said antenna circuit is lower than any frequency to which said resonant circuits are tunable, a winding inductively coupled to said second resonant circuit connected in series with a fixed capacitor between the low-potential side of said first resonant circuit and ground, and an adjustable capacitor connected between said antenna and the low-potential side of said first resonant circuit.

12. A preselector system for a superheterodyne receiver including a fixed-tuned antenna circuit and a pair of resonant circuits each having variable tuning capacitance, one of said resonant circuits having first and second serially connected but magnetically uncoupled inductors,

the first of said inductors being coupled to said antenna circuit the second of said inductors being inductively coupled to the other of said resonant circuits, and a capacitor so connected between said antenna circuit and the junction of said inductors and so proportionedas to materially increase the discrimination of said system against signals of image frequency.

DWIGHT V. SINlfTINGER.

January 25, 19

DWIGHT V. SINNINGER,

It is hereby certified that error appears in the printed. specification of the above numbered patent requiring correction as follows Page 5, first column; line I 6, claim 5, after the word "circuits" insert a comma: same page, second column,v line 5L -55, claim 8, for "inductice-capacitive" read inductive-capacitive; andthat the said Letters Patent should be readwith these corrections therein that the same case in the Patent Office.

I may conform to the record of the Signed and sealed this let day of March, A. D. 1958.

(Seal) Henry Van Arsdale, I Acting. Commissioner of Patents.

ed from the high-potential sides to the low-potential sides of said resonant circuits to align said resonant circuits, combined inductive and capacitive coupling means between said antenna and said first resonant circuit including a reactor such that the natural frequency of said antenna circuit is lower than any frequency to amplifier, said system including an antenna circult and first and second resonant circuits, each of said resonant circuits having a high-potential side anda low-potential side, variable capacitors connected from the high-potential sides of said resonant circuits to ground for tuning said resonant circuits, an adjustable capacitor connected from the high-potential side to the low-potential side of said second resonant circuit to align said resonant circuit, combined inductive and capacitive coupling means between said an- Patent 'No. 2,106,229,

CERTIFICATE OF CORRECTION.

tenna and said first resonant circuit includinga 'reactor such that the natural frequency of said antenna circuit is lower than any frequency to which said resonant circuits are tunable, a winding inductively coupled to said second resonant circuit connected in series with a fixed capacitor between the low-potential side of said first resonant circuit and ground, and an adjustable capacitor connected between said antenna and the low-potential side of said first resonant circuit.

12. A preselector system for a superheterodyne receiver including a fixed-tuned antenna circuit and a pair of resonant circuits each having variable tuning capacitance, one of said resonant circuits having first and second serially connected but magnetically uncoupled inductors,

the first of said inductors being coupled to said antenna circuit the second of said inductors being inductively coupled to the other of said resonant circuits, and a capacitor so connected between said antenna circuit and the junction of said inductors and so proportionedas to materially increase the discrimination of said system against signals of image frequency.

DWIGHT V. SINlfTINGER.

January 25, 19

DWIGHT V. SINNINGER,

It is hereby certified that error appears in the printed. specification of the above numbered patent requiring correction as follows Page 5, first column; line I 6, claim 5, after the word "circuits" insert a comma: same page, second column,v line 5L -55, claim 8, for "inductice-capacitive" read inductive-capacitive; andthat the said Letters Patent should be readwith these corrections therein that the same case in the Patent Office.

I may conform to the record of the Signed and sealed this let day of March, A. D. 1958.

(Seal) Henry Van Arsdale, I Acting. Commissioner of Patents. 

